JPH0338704B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to reducing or eliminating undesirable shunt currents in electrochemical devices such as storage batteries, and more particularly to:
This invention relates to improvements in protective electrodes for electrochemical devices for reducing or eliminating shunt current by applying a nulling voltage.

It is known that in all types of electrochemical devices, especially in batteries with multiple cells arranged in a common electrolyte, shunt current losses occur due to conductive bypass paths that occur in the electrolyte surrounding the cells. There is. Such shunt current losses occur constantly in such devices during charging, discharging, and under open circuit conditions, and can have undesirable side effects and shorten the useful life of the device. .

One method for eliminating shunt currents is disclosed in U.S. Pat. No. 4,197,169, in which a protective erase current is applied to a common electrolyte in a common manifold arrangement. . The present invention is based on the teachings of this patent, which are also incorporated herein by reference.

When applying such a protective current, especially in a system characterized by circulating electrolyte, an electrode is required that does not interfere with the electrolyte flowing through the manifold. The simplest and most effective electrode structure from a hydraulic point of view is a thin wire electrode placed in the center of the flow system. This electrode produces virtually no pressure drop. However, this type of electrode applies current from a point source;
Therefore, the current density distribution in the manifold near the electrodes is non-uniform, and the current density spreads along the length of the manifold. Devices with a point source or focal electrode structure are P.
``Electrochemical Generators With Auxiliary Cathode'' by Durand.
U.S. Patent No. 1 for “Auxiliary Cathode”
No. 4136232 (patented on January 23, 1979), and J.
U.S. Patent No. 4,081,585 (patented March 28, 1978) entitled "Forced Flow Electrochewical Battey" by Jacquelin.
seen in

The electrode by Gacquelin and Durand is constructed to produce a finite amount of zinc metal and is designed to facilitate cleaning in an electrolyte fluid. However, because point source electrodes are used, the current density along the manifold is non-uniform and is not equal to the shunt voltage. Therefore, by using these devices, shunt current will not be effectively reduced.

The present inventors first used mesh-like electrodes to
The intention was to provide a substantially uniform current density to the manifold while not impeding fluid flow. Although such electrode configurations may work well in some cases, there are cases where it is required to supply reactants to the electrolyte solution or to remove certain undesirable products from the electrolyte solution. is not practical. For example, in electrolytic cells, it is desirable to remove oxygen buildup in the hydrogen producing electrolyte to prevent potential explosions. Furthermore,
In some cases, the fluid pressure drop caused by the mesh is undesirable.

After careful consideration by the inventors of all possible electrode configurations, the use of annular electrodes was considered the most practical. The ring electrode is
The protective current is placed around the manifold in such a way that it does not impede fluid flow in all or part of the system using the circulating electrolyte and provides a substantially uniform current density distribution to the electrolyte along the manifold at all times. can be granted.

Furthermore, the annular electrode can be equipped with means for injecting and removing reactants and/or products from the electrolyte.

Another benefit of providing a guard current around the manifold (which current has a uniform current density distribution) is that the power required to maintain the erase current is reduced.

The reduction in power consumption by using the annular electrode structure is due to the fact that other electrode structures require the electrodes to be placed a long distance along the manifold from each cell that generates the current. It is. At such a long distance,
The current must spread radially from the point source to match and cancel the shunt voltage at each cell location. However, because point source electrodes require current to flow over long distances through the electrolyte, increased voltage and therefore increased power is required for such point source or focal electrode configurations. Become. In contrast, annular electrodes provide a substantially uniform pattern of current lines in the manifold and require less power because they can be placed closer to the cells.

Furthermore, since the applied electrode voltage is also a function of the current density, increasing the surface area with the annular electrode structure is preferable from the standpoint of current density and power.

The present invention includes at least one common manifold, a plurality of cells fluidly connected through the one manifold, and a plurality of cells disposed in the one common manifold and creating an undesirable shunt current. The present invention relates to an electrochemical device having a common electrolyte of the cells providing an electrolytic conductive bypass path around the cells and at least one electrode providing a protective shunt current through the electrolyte in the common manifold. The manifold holds an electrolyte that provides a conductive bypass path around the cell. This bypass can then create undesirable shunt currents.

At least one annular guard electrode supported by the manifold provides a guard current around the manifold, the current density distribution being substantially uniform in the electrolyte along the manifold. This uniform current density distribution effectively reduces or eliminates shunt current while minimizing the power consumed thereby.

For the purposes of this description, an "annular electrode" refers to a radial cross-section (e.g., circular, oval, or polygonal inner wall cross-section) surrounding the manifold.
means all such electrodes. Furthermore,
An annular electrode may have a parallel, curved, tapered, or irregular axial cross-sectional shape. By using such different shapes, it is possible to control the flow of the electrolytic solution and the current density distribution depending on the purpose. However, a circular radial cross-section and a tapered axial cross-section are probably the preferred shapes.

The term "uniform current density distribution" above refers to a condition in which the protective current line (the line representing the strength of the protective current) is substantially uniform across the cross-section of the electrolyte fluid over substantially the entire length of the manifold. This means that the voltage drop across each cell is substantially equal to the shunt voltage of that cell.

In addition, the term electrochemical device means the following: photoelectrochemical device, storage battery (primary battery or secondary battery), fuel cell, chlor-alkali battery, electrowinning device, electrorefining device, Electrolyzers, electrochemical reactors, monopolar or bipolar devices, and devices with circulating or non-circulating electrolytes.

The "common electrolyte" used in this specification is
An electrolyte used and distributed in two or more cells so as to form a physical continuum. In circulating electrolyte systems using one or more manifolds, the physical continuum includes the electrolyte contained in the manifolds, branch channels, and cells. In a static electrolyte system, the physical continuum includes the electrolyte contained in the cell-to-electrolyte connection region (eg, above and around the cell).

The “distributed electrolyte” used herein is
It shall mean the portion of the electrolyte that is located in a region common to the electrolytes contained in the individual machine components. Therefore, in a circulating electrolyte system using one or more manifolds, the electrolyte contained within the manifold is the distributed electrolyte and is not contained in branch channels, cells, or other individual components. The electrolyte used is not a distributed electrolyte. In a static electrolyte system, the distributed electrolyte is the electrolyte contained in the header space and/or common base area of the device, and in each cell and other individual components. The electrolyte is not a distributed electrolyte.

More specifically, the present invention relates to a device that utilizes the application of a protective current by an annular electrode to an electrolytically conductive bypass path when the electrochemical device is in operation. The device has cells coupled at least partially in series and includes a common electrolyte and a distributed electrolyte common to at least two of such cells, thus distributing the electrolyte around and around the cells. An electrolytically conductive bypass path occurs through the distributed electrolyte, resulting in undesirable shunt currents in the absence of such protective currents.

Minimizing the shunt current by providing a protective current by means of an annular electrode can also be taken in electrochemical devices with non-circulating electrolyte.
In this case, the electrolyte can be kept stationary (or at least not wanted to be transported or circulated for some time), and this electrolyte is common to at least two of the cells in series, i.e. , forming a physical continuum, thus creating an electrolytic conduction bypass path through the electrolyte around cells having a common electrolyte, resulting in undesirable shunt currents. The conductive bypass includes the distributed electrolyte and may be present in the electrolyte above the cell or through a separate common element such as a base, fill tube, manifold, etc.
In both cases, the means for applying the protective current are constituted by annular electrodes arranged outwardly from the cell and in the distributing electrolyte at each end of the bypass path in the electrolyte. Thus, by applying a protective current through the bypass path,
Minimization of shunt current is effectively achieved.

In a preferred embodiment of the invention, as shown in FIG. This causes circulation of the electrolyte within the device, creating an electrolytically conductive bypass through the distributed electrolyte and creating a shunt current. An annular electrode is provided to provide a protective current through the one or more manifolds (ie, through the distributed electrolyte portion of the conductive bypass path) to minimize shunt current. The protective current provided by the annular electrode has a substantially uniform density through the distributed electrolyte within the manifold, and therefore through the branch channels connecting the cells to the manifold. , which acts to minimize the formation of shunt currents while minimizing power consumption. Thus, a change from electronic conduction to electrolytic conduction occurs. Since the oxidation/reduction reactions at these electrodes change electronic conductivity to ionic conductivity, any redox reaction can be used, at least in principle. For example, such a reaction can be the same as an electrode reaction in an electrochemical device. Alternatively, other reactions that are chemically and electrically compatible with the electrochemical device can also be used.

For example, H ₂ may be oxidized by an anodic reaction at one end of the electrochemical device, and H ₂ may be generated at the other end. These two reactions in an acidic solution are: H ₂ → 2H ⁺ +2e (anode) 2H ⁺ +2e → H ₂ (cathode) The H ₂ gas produced can be captured and returned to the anode.

Alternatively, bromide is oxidized at one electrode and bromine is reduced at the other electrode.

2B ^- →Br ₂ +2e 2e+Br ₂ →2Br ^-In yet another case, O ₂ is oxidized at the anode,
A reaction that is reduced at the cathode is applied.

O ₂ +4H ⁺ +4e→2H ₂ O 2H ₂ O→O ₂ +4H ⁺ +4e The choice of redox reaction depends on the particular system to be protected and can be selected according to general electrochemical considerations.

The electrochemical device used in the specification of the present invention is
In the simplest case, it means a plurality of cells, at least some of which are connected in series. However, the electrochemical device of the present invention may be such a device,
Furthermore, it is of a larger scale and includes two or more blocks of cells electrically coupled in series, with a common electrolyte being supplied to and removed from the parallel blocks by a main manifold. It may also be a device that Thus, each cell block may consist of two or more cells in series, to which electrolyte is supplied in parallel from a secondary manifold provided in each cell block. In such a system, there will be shunt current within the block through the block manifold (minor manifold) and shunt current between cell blocks through the main manifold. Such shunt currents may be minimized, if desired, by guard currents in the block manifold and the main manifold.

To apply protective current through a manifold, two electrodes are generally used (one positive and one positive).
(the other being the negative electrode), it is necessary to cause an electrochemical reaction to flow the current. Factors that must be considered include: If there is not a sufficient amount of reactant in the electrolyte provided in the manifold, the reactant must be supplied from an external source. In addition, if the reaction products at the protective electrode are unfavorable to the electrolyte,
Such products must be removed.

As discussed in more detail below, the annular guard electrode may be configured with a liner by which necessary reactants can be replenished and/or undesired products removed.

In FIG. 1, electrodes 52, 52', 54, 56
The annular guard electrode shown as and 58 may be of any of the types described above, as explained below. The protective current was applied in accordance with the present invention by an annular electrode connected to a group of series-coupled zinc-bromine monopolar cells as illustrated in FIG. In FIG. 1, protective electrodes 52, 56, 5
4', 58' are arranged in the main stream of the electrolyte flow of the system and form an annular structure. Protective electrodes 54, 58, 5
2', 56' may be flat, i.e.
The electrodes may not be included in the flow system of the device. However, in view of heat and product considerations, it may be desirable for the electrolyte to pass through these protective electrodes, and in such cases a ring-shaped structure may be adopted.

A storage battery device having eight series-coupled cell groups is shown as 10. Cell 12 is representative of the cell group and includes an anode 14 and a cathode 16. Anolyte (arrow 11) is channel 2
0 into the chamber 18 of the cell 12 and the catholyte (arrow 13) flows through the channel 24 into the cell 12.
into the chamber 22. Chambers 18 and 22 are separated by an ion permeable membrane separator 26. Cell 12 is connected to adjacent cell 2 by electrical connection means 30.
8 in series. Terminal cells 12 and 12' are connected to terminal terminals 34 and 3, respectively.
Contains 6. Anolyte entry into chamber 18 through channel 20 is provided by a distribution electrolyte manifold 38, which supplies anolyte to all cells. The anolyte exits the chamber 18 by a channel 40 (arrow 15) and further through a distribution electrolyte manifold 42 from which all the anolyte exits as well. The flow of catholyte into chamber 22 through channel 24 is via a distribution electrolyte manifold 44, which supplies catholyte to all cells. The exit of the catholyte from the chamber 22 (arrow 17) takes place via a channel 46 and further through a distribution electrolyte manifold 48 through which all the catholyte exits.

Annular electrodes 52, 52', 54, 54', 56, 56', 5 for providing protective current to this device 10
8, and 58' are generally provided at each end of the four manifolds 38, 42, 44, and 48 to contact the distributed electrolyte. The anolyte manifolds 38 and 42 have protective current negative electrodes 52 and 52', respectively, and
Each has a protective current positive electrode 54 and 54'. Catholyte manifolds 44 and 48
are protective current negative electrodes 56 and 5, respectively.
6′, and positive electrodes 58 for protective current, respectively.
and 58'. For example, a guard current may be applied between negative electrode 52 and positive electrode 54 to pass the guard current through the dispensing electrolyte through manifold 38, thereby passing through a conductive bypass (i.e., through manifold 38). (through channels connected to the manifold and through the manifold). Similarly, a protective current is applied across manifolds 42, 44 and 48 and into the distributed electrolyte.

While the system is in operation, both anolyte and catholyte are circulated through their respective manifolds, channels and chambers and recirculated from a storage device (not shown).

As mentioned above, the monopolar cells of device 10 are coupled in series electrically and in parallel in terms of fluid flow. When no protection current is applied in accordance with the present invention, significant shunt currents occur in the channels and manifolds. In this zinc-bromine system, shunt current not only causes a loss of system performance and waste of components, but also causes the anolyte to flow into and out of the zinc electrode chamber. This will result in zinc growth at many points on the electrode.

Each of the protective annular positive electrodes 54, 54', 58 and 58' in the zinc-bromine system shown in FIG. 1 can be constructed from carbon and/or graphite annular sleeves. The electrolyte is
It flows through annular electrode sleeves 54' and 58' in manifolds 42 and 48, respectively (see arrows 19 and 21). A typical sleeve surface 58' is sufficiently corrosion resistant to oxidize Br ^- to Br ₂ over an extended period of time. Current collection may be accomplished by a current collector 64 made of tantalum wire. In other cases, the wire current collector 64 may be made from other materials, such as platinum or carbon, and such materials may be more compatible with the particular reaction of the device. . Similarly, the protective positive electrode sleeve 58' may be constructed from other materials that may be more compatible with a variety of electrochemical reaction devices. Such materials can be selected from a wide variety of materials, such as carbon, graphite, metallized carbon, ruthenium-titanium, etc., for use in zinc-bromine battery systems. The inner walls 50 and 51 of protective positive electrode sleeves 62 and 64 may be dimensioned to be coplanar with manifolds 42 and 48, respectively. Metallized
Carbon's M-14 and Airco Speer's
Grade 580 can be used as the material for the positive electrode.
A similar requirement exists for sleeves 54 and 58 of manifolds 38 and 44, respectively.

The protective annular negative electrodes 52, 52', 56 and 56' in the zinc-bromine system shown in FIG. 1 may have a more complex structure than their respective protective positive electrodes. The electrolyte is placed in each manifold 3.
8 and 44 (see arrows 23 and 25). The structure of a typical annular electrode 56 is shown in detail in FIG.

Protective annular negative electrode 56 consists of an outer sleeve 70 and an inner porous liner 72. The inner wall 74 of the liner may be flush with the inner wall 76 of the manifold 44 to minimize fluidic pressure drop losses. Sleeve 70 is made of carbon and/or graphite material (e.g., M-14 from Metallized Carbon, or
Carbon Technologies' Grade 101). Ruthenium-titanium alloy (Ruthenized Tifanium) of similar quality may also be used.

The sleeve 70 is supplied with a bromine-rich electrolyte, for example via a tube 78 (see arrow 71). The bromine-rich electrolyte comes from a storage device (not shown). The bromine-rich electrolyte is then returned to the storage device via tube 82 (see arrow 73). The purpose of flowing the bromine-rich electrolyte through the sleeve 70 is to supply bromine ions (Br ^- ) to the electrolyte flowing through the annular electrode 56 and into the manifold 44 . The internal porous sleeve 72 is intended to ensure that substantially only bromine ions (Br ^- ) enter the electrolyte, and thus this liner will not cause the aforementioned bromine-rich electrolyte to enter the electrolyte. Prevent or delay the inflow of liquid. Thus, liner 72 is designed to conduct ionic current with low resistance.

Liner 72 may be constructed from sintered microporous polypropylene. The pores of liner 72 can then be filled with ion exchange material.

Liner 72 may also be constructed from other microporous, ion-selective plastics or ceramics depending on the particular chemistry of the system employed. For example, in the anode 14 and the cathode 16,
In the electrolytic system that generates oxygen and hydrogen, respectively, hydrogen is generated by guard electrode reactions at electrodes 52, 56, 52' and 56', and 54, 5
8, 54' and 58' to allow oxygen to be evolved by guard electrode reactions. The reaction at guard electrodes 56 and 56' thus causes hydrogen to be introduced into the cell system product, the oxygen-containing electrolyte. Similarly, the protective electrode 54
The reaction at and 54' introduces oxygen into the stream containing the hydrogen product. In some cases, such mixtures may be undesirable, ie explosive mixtures may be formed.
Therefore, the use of a liner 72 to separate and remove such undesirable products from the system would be useful. Guard electrode reactions at electrodes 52 and 52' produce hydrogen, and guard electrode reactions at electrodes 58 and 58' produce oxygen. The above reaction is compatible with such systems since hydrogen and oxygen are added to the electrolyte where hydrogen and oxygen evolution of the system is occurring, respectively. In this case, there is no requirement for liner 72. The composition of liner 72 in this case is such that it is compatible with electrolytic reactions.

At the protective annular negative electrode 56 of FIG. 2, a current is applied to the graphite 70 through a tantalum wire 84, which reduces Br ₂ to Br ^- .
Other wire materials are also possible as mentioned above.

In supplying the bromine-rich electrolyte to sleeve 70, the flow may be continuous or intermittent.
However, it must match or be in excess of the stoichiometry of the electrode current.

3a to 3d show different possible radial cross-sections for the inner wall of the annular electrode. Figure 3a shows an annular electrode with a conventional circular cross section. Figures 3b, 3c and 3d are oval, hexagonal and square, respectively, although not all shapes are shown by these figures. Thus, the purpose of making the radial cross section various shapes is for the following reasons: (a) to match the shape of the manifold; (b)
Varying the flow characteristics of the electrolyte (c) Provides a different current density distribution along the manifold, thus causing each cell to have a shunt voltage drop commensurate with the voltage at the cell location in the manifold.

Similarly, annular electrodes with conventional parallel inner walls (as shown in FIG. 2) are prepared in FIGS. 4a and 4b.
It may also be designed with different axial cross-sections as shown in Figures 4c and 4c. That is,
FIG. 4a shows a tapered inner wall, FIG. 4b shows a curved inner wall, and FIG. 4c shows an irregularly shaped inner wall. The reason why annular electrodes with various axial cross sections are designed in this way is for the same purpose as mentioned above.

As can be understood from the above design changes, "annular electrode" is not necessarily intended to mean an electrode having a straight cylindrical shape.

The above-mentioned materials suggested as electrode parts are generally applicable to the zinc-bromine system. However, the present invention
It is not intended to be limited to such zinc-bromine systems or to such specific materials. It will be understood by those skilled in the art that similar or different materials may be used for other systems and reactions. Accordingly, the present invention includes such obvious modifications.

[Brief explanation of drawings]

FIG. 1 illustrates an example of an electrochemical device according to the invention, in which eight monopolar cells are coupled in series and two ring electrodes are provided in each of four common manifolds. FIG. 2 is a cutaway perspective view of a protective annular negative electrode according to the present invention positioned adjacent to the common manifold of FIG. 1; Third
Figures a to 3d show examples of possible radial cross-sectional shapes of annular electrodes according to the invention. Chapters 4a-4
Figure c shows an example of a possible axial cross-sectional shape of an annular electrode according to the invention.

Claims (1)

Claims: 1. at least one common manifold, a plurality of cells fluidly connected through the one manifold, and an undesirable shunt current disposed in the one common manifold; an electrochemical device having a common electrolyte of the cells that provides an electrolytic conduction bypass path around the cells that produces a The electrodes are supported by the one common manifold and provide a protective current around the manifold having a substantially uniform current density distribution along the manifold and through the electrolyte while minimizing power consumption. An electrochemical device characterized in that it is a ring-shaped protective electrode adapted to effectively reduce shunt current. 2. The electrochemical device according to item 1, further comprising means for circulating the electrolytic solution through the annular protective electrode and the manifold. 3. The electrochemical device according to item 1, wherein the annular guard electrode is substantially porous. 4. The electrochemical device according to item 1, having two annular guard electrodes supported by the manifold. 5. The electrochemical device according to item 1, wherein the annular protective electrode is made of a selectively permeable material. 6. The electrochemical device of claim 1, wherein the annular guard electrode comprises a sleeve with a porous inner liner.